This plugin basically logs you off the server once the countdown has happened. It's not at all a complex plugin but people were requesting a working 1.7/1.8 version so here it is and it's fully configurable!
/Logout - Logs you off the server!
logout.logout - Allows you to do /logout!
Prefix: '&9&l&oLogout&7| '
LogoutCountdown: '&8&lYou will be logged out in... &c&l'
LogoutMessage: '&aYou were logged out safely!'